"Fine" radial adjustment boring quills, e.g. with a radial adjustment range of 0.005-0.010", are known in the art where adjustment is effected through an eccentric sleeve or ring having cylindrical O.D. and I.D. axial centers offset up to 0.005" providing up to 0.010" radial adjustment over a 180.degree. rotation of the eccentric bushing within the circular bore of an adapter. A commercial tool of this type, known in the trade as a "Briney Precision Adjustment Tool", has an adjustment eccentric bushing calibrated relative to an adapter body to indicate radial quill position responsive to bushing rotation which may be effected rapidly without loosening any clamping or set screw element.
In such fine adjustment tools, adjustment of the boring bar causes the quill machining point to move in an arcuate path changing slightly its rake angle to a workpiece surface. The small dimensional change involved in such fine adjustment renders the magnitude of change in rake angle correspondingly small and relatively insignificant as far as cutting action at the boring point. However, a coarse adjustment, e.g. in the order of 0.100-0.125", effected through such conventional eccentric bushing adjustment would involve an unacceptable or undesirable change in rake angle for many boring applications. Accordingly, for coarse radial adjustment of a boring quill it is desirable if not essential to effect movement of the tool point along a fixed linear centerline at all times throughout minimum to maximum adjustment without change in radial rake.
In certain of the "Briney" tools a coarse radial adjustment has been provided through the provision of a transverse key slot in the tool holder for retaining a transverse square bar with a cutting insert at its end which may be adjusted manually and held by set screw or by clamping the key slot.
An eccentric boring head disclosed in U.S. Pat. No. 2,780,467 provides a coarse adjustment feature which maintains a linear path of adjustment through the use of a T-slot in an adapter engaged by a T-head in the tool carrying member received slidably within the T-slot. The tool carrying member has a threaded cylindrical surface on which a lock nut may be tightened to draw shoulders of the T-head into tight engagement after linear adjustment is effected through an eccentric ring. The lock nut must be loosened to permit rotation of the eccentric ring and retightened after each adjustment. A fine adjustment feature provided in the disclosure of the '467 patent also requires loosening of lock and set screws to permit an adapter to be rotated in the body of the tool.